The present invention generally relates to rotating electromagnetic components, such as rotors for motors and generators. More particularly, this invention relates to a method for mass-producing reluctance motor rotors having soft magnetic regions separated by hard (permanent) magnetic, soft magnetic or nonmagnetic (nonferromagnetic) regions that serve as flux barriers to the soft magnetic regions.
Synchronous reluctance motors are a desirable alternative to electric motors and generators of the inductance type in terms of improved efficiency. While the stator of a reluctance motor is similar to that of an induction motor, its rotor is significantly more complex, requiring two axes of widely differing magnetic reluctance. For this purpose, reluctance rotors are often formed to have at or near its perimeter alternating regions of soft magnetic material and either nonmagnetic material or magnetized hard magnetic material. Various methods have been proposed for manufacturing reluctance rotors, with radial laminated cores formed of thin soft iron sheets being the typical approach. However, radial lamination methods have not proven desirable for high-volume manufacturing due to the labor intensity of the lamination process, as well as other process complexities and complications. Due to the complexity of reluctance rotors, conventional powder metallurgy methods have generally been found to be impractical for mass production. Furthermore, reluctance rotors formed by powder metallurgy with low core losses have typically lacked sufficient strength to operate at high rotational speeds.
In view of the above, it would be desirable if an improved manufacturing process were available that enabled the mass production of reluctance rotors.
The present invention is directed to reluctance rotors and a method for manufacturing reluctance rotors having soft magnetic regions separated by regions that serve as flux barriers to the soft magnetic regions. The method of this invention generally entails producing a generally cylindrically-shaped body having a central axis and an outer peripheral surface. The body is composed of concentric regions, at least one of which is a soft magnetic region while at least a second region of the concentric regions is formed of a material with dissimilar magnetic properties to the soft magnetic region, e.g., hard (permanent) magnetic, soft magnetic or nonmagnetic (nonferromagnetic) materials. Some or all of the concentric regions can be formed by powder metallurgy techniques. Once formed, the body is divided along radials thereof to form wedge-shaped members, with each wedge-shaped member having coaxial arcuate regions that are portions of the concentric regions of the body. As a result of the manner in which the body is divided, the wedge-shaped members have radial surfaces defined where the wedge-shaped members were divided from the body, and each wedge-shaped member also has a distal surface corresponding to the outer peripheral surface of the body. The wedge-shaped members are then arranged about an axis of symmetry corresponding to the axis of rotation of the rotor, with the distal surfaces of the wedge-shaped members disposed adjacent the axis of symmetry and facing each other, and with the radial surfaces of the wedge-shaped members facing away from the axis of symmetry. The wedge-shaped members are then bonded together and machined if necessary to form the rotor of the reluctance motor.
In view of the above, the process of this invention can be seen to produce a reluctance rotor without a complicated radial lamination process using sheets of different materials. Instead, the rotor of this invention is produced by reassembling wedge-shaped members cut from a preformed body that preferably contains all of the magnetic components of the rotor. Notably, the process of this invention entails fewer steps than required by prior art radial lamination methods, and greatly reduces the amount of scrappage and machining that is often required after the rotor has been assembled. The process of this invention also offers the benefits of lower production costs by eliminating stamping dies, and is capable of producing rotor assemblies with lower weight than prior art laminated assemblies. In applications where individual particles of the powder or powders are insulated with an encapsulation material, lower iron loses result, resulting in lower rotor temperatures, improved motor/generator efficiency and reduced cooling requirements. The result is a process that is practical for the mass production of reluctance rotors.
Other objects and advantages of this invention will be better appreciated from the following detailed description.